Radio frequency identification tags and radio frequency identification tag systems are known, and find numerous uses. For example, radio frequency identification tags are frequently used for personal identification in automated gate sentry applications protecting secured buildings or areas. Information stored on the radio frequency identification tag identifies the person seeking access to the secured building. Older systems require the person accessing the building to insert or swipe a programmed identification tag into or through a reader for the system to read the information from the identification tag. A radio frequency identification tag conveniently reads the information from the radio frequency identification tag at a small distance using radio frequency ("RF") data transmission technology eliminating the inserting or swiping operation. Most typically, the user simply holds or places the radio frequency identification tag near a base station, which is coupled to a security system securing the building or area. The base station transmits an excitation signal to the radio frequency identification tag that powers circuitry contained on the radio frequency identification tag. The circuitry, responsive to the excitation signal, communicates the stored information from the radio frequency identification tag to the base station, which receives and decodes the information. The read information is communicated to the security system and, if appropriate, access is granted to the individual. In general, radio frequency identification tags are capable of retaining and, in operation, transmitting a substantial amount of information--sufficient information to uniquely identify individuals, packages, inventory and the like.
A typical technology for powering and reading a radio frequency identification tag is inductive coupling or a combination of inductive power coupling and capacitive data coupling. Inductive coupling requires incorporating a coil element into the radio frequency identification tag. The coil element is excited (or "energized") by an excitation signal from a base station to provide power to the radio frequency identification tag circuitry. The radio frequency identification tag coil, or a second tag coil, may be used to transmit and receive the stored information between the radio frequency identification tag to the base station. Inductive coupling technology is relatively expensive, particularly for applications where it may be desirable to have a disposable radio frequency identification tag such as in an inventory management application. Radio frequency identification tags relying on inductive coupling are also sensitive to orientation of the radio frequency identification tag with respect to the base station since the field created by the excitation signal must intersect the coil element at substantially a right angle for effective coupling. Furthermore, read ranges for inductively coupled devices are generally on the order of several centimeters. Longer read distances are desirable, and for certain applications, such as electronic animal identification, baggage tracking, parcel tracking and inventory management applications, are necessary.
Other radio frequency identification tag technologies include magnetically coupled, magnetically and electrostatically coupled technologies. While offering certain performance enhancements, and in some cases cost advantages, over inductive coupling technology, read ranges with these other technologies remain unacceptably short. For example, in an electronic article surveillance ("EAS") system, it is necessary to read the radio frequency identification tag as it passes through a standard doorway. Similarly, because of the vast differences in sizes of parcels and baggage an ability to read the radio frequency identification tag at a substantial distance is imperative. As will be further appreciated orientation of the radio frequency identification tag with respect to the base station can not be prearranged, and therefore, can not be allowed to substantially effect read distances. Each of the mentioned technologies tends to be overly orientation sensitive.
Magnetic coupling technologies have found some success in EAS systems by providing sufficiently large read ranges. For example, a magnetic strip and detection technology is available from 3M of St. Paul, Minn. (sold under the product name "Tattle Tape"). The magnetic strips are small and thin thus allowing for easy insertion within the pages or spines of books, jewel cases of CDs, and the like. Magnetic strip technology, however, is information limited. That is, the magnetic strips are capable of providing only a single bit of information--typically indicating authorization yes/no for removal from the secured area. Magnetic strip technology is not capable of providing a sufficient amount of data for unique identification, and as such, is not suitable for automated inventory applications.
Magnetic strip technology is also not suitable for applications where the protected media is magnetic in nature. The magnetic strip is coded and decoded by subjecting the strip to a magnetic field. Subjecting magnetically recorded media, such as videotape, recorded audio tape, computer diskettes, and the like to magnetic fields may damage the recorded media. Another important consideration for EAS system operation is read time. A person attempting to illegally remove an article from a secured area is likely not to pause while passing through a sensing area of the surveillance system to allow the system time to read the surveillance tag. Magnetic strip technology offers fast read times; however, radio frequency identification tag systems may not offer sufficiently fast read times, e.g., tag excitation, data transmission, data verification and finally authorization, to be effective in EAS systems.
Still, radio frequency identification tag technology offers the significant advantage of storing and conveying sufficient information so as to uniquely identify persons, retail articles, parcels, packages, baggage and the like. However, radio frequency identification tag technology is limited in application by cost, read range and read time. Magnetic strip technology offers the advantage of long read range, and based upon the limited amount of data conveyed, fast verification. But because of the limited amount of information it is capable of conveying, magnetic strip technology is limited in application.
Thus, there is a need for an improved radio frequency identification tag.